This invention relates to a device and method for use in the taking of moulds or like three-dimensional impressions of feet.
Foot orthotics are an essential part of conservative orthopaedic treatment for correction of biomechanical abnormalities, congenital deformities and abnormal positions acquired through accident or disease processes. The taking of accurate plaster of Paris moulds or three-dimensional impressions of feet is a necessary part of the process of manufacture of foot orthotics.
At present, the plaster of Paris casts and three-dimensional impressions of feet are taken in the following positions:
With a patient sitting with the knee extended, or lying in a prone or supine position, the clinician palpates the subtalar joint to a neutral position with one hand, whilst the remaining hand applies dorsiflexory pressure to the fifth metatarsophalangeal joint or to the plantar surface of the webbing of the fourth and fifth toes.
Alternatively, with a patient sitting with the knee flexed, the foot is allowed to semi-weight bear whilst the clinician maintains the subtalar joint in a neutral position with one hand, as the plaster of Paris bandage or three-dimensional moulding material is placed around the foot and hardens.
A major problem with conventional methods of making casts and impressions of feet is their inherent lack of reproducibility. This can lead to the production of ill-fitting orthotics which may be uncomfortable and/or detrimental to the user.
There has now been devised a device and method for use in the taking of moulds and three-dimensional impressions of feet which overcome, or substantially mitigate, the above-mentioned or other disadvantages.
According to a first aspect of the invention, a device for use in the taking of a mould or impression of a foot comprises a generally planar member adapted for abutment with the sole of a patient""s foot, and means by which the device may be held in any desired orientation.
According to a second aspect of the invention, a method of taking of a mould or impression of a foot comprises applying to the sole of the foot the planar member of a device as defined above, and holding the device in a desired orientation.
According to a third aspect of the invention, a device for use in the taking of a mould or impression of a foot comprises a generally planar member adapted for abutment with the sole of a patient""s foot, and means for detecting angular displacement of the planar member,
According to a fourth aspect of the invention, a method of taking of a mould or impression of a foot comprises applying to the sole of the foot the planar member of a device as defined above, and detecting the angular displacement of the planar member.
In a preferred embodiment, the device according to the invention is provided with angular measurement means and display means, by which angular displacement of the planar member from a datum position can be determined. In one preferred embodiment, such means may be electronic. In such a case, means for setting the display to zero to provide a datum are preferably provided. This means may be push button actuatable by the clinician, to facilitate measurement of a given angular displacement from the datum position. Alternatively, the angular measurement and display means comprises a Vernier scale arrangement.
The angular measurement means may comprise means by which movement in degrees of tilt in the frontal plane of the foot may be measured by mechanical and/or magnetic and/or rotational movement. The angular measurement means may, for instance, include means for detecting a reference and means for determining the position of the vertical plane in relation to that reference. The reference may comprise another part of the foot or leg, or may be an external reference such as magnetic north, a mechanical reference means, or may be provided by means of a gyroscope. A potentiometer may be provided which is rotated when the device is rotated, thereby changing the resistance of the potentiometer. The resultant change in voltage may, after suitable calibration, be converted by digital logic to an output value in degrees which is displayed, e.g. on a liquid crystal display. A separate moving axis may be added to the planar member or built into the planar member to act as a reference point, or a fixed point strapped to the leg or foot or otherwise fixed, e.g. to the patient""s chair, may extend to the planar member.
The new device can be used with the patient seated with the knee extended, or with the patient lying in a prone or supine position.
The planar member may be hingedly connected to one or more further planar members to allow separate forefoot and rear foot movement and first ray movement of the foot to be detected.
The device according to the invention is advantageous primarily in that it facilitates more accurate taking of three dimensional impressions of feet, which is currently carried out manually holding the foot whilst the plaster hardens to form the cast. The accuracy of alignment may be within a single degree or better. The device provides greater stability whilst the mould is being taken and, in preferred embodiments, any movement of the patient""s foot or the clinician""s hand will be visibly seen on the liquid crystal display, enabling the position to be corrected. This is especially important when taking moulds of children""s feet.
The device also reduces or eliminates the need for adding estimated amounts of intrinsic posting to the positive cast, which is time consuming and a major source of inaccuracy in the finished orthosis.
The device may be used for the manufacture of both foot orthoses and ankle/foot orthoses. The device can be used for a three-dimensional impression of a foot, when using impression materials or impression bagging materials which surround the foot, whilst the clinician can check the angular position of the foot at any time.
The device thus improves both the reproducibility and accuracy of three dimensional impressions of feet.